Sign change in the tunnel magnetoresistance of Fe3O4/MgO/Co-Fe-B magnetic tunnel junctions depending on the annealing temperature and the interface treatment

Marnitz, Luca; Rott, Karsten; Niehörster, Stefan; Klewe, Christoph; Meier, Daniel; Fabretti, Savio; Witziok, Matthäus; Krampf, Andreas; Kuschel, Olga; Schemme, Tobias; Kuepper, K.; Wollschläger, J.; Thomas, Andy; Reiss, Günter; Kuschel, Timo

doi:10.1063/1.4917018

Cited by 22 publications

(23 citation statements)

References 42 publications

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“…Especially, thin magnetite films (Fe 3 O 4 ) have attracted intensive research interest in the last decade in the field of spintronics [2] and spin caloritronics [3,4]. Due to their anticipated half-metallic behavior with complete spin polarization at the Fermi level [5] and high (bulk) Curie temperature of 858 K [6], thin magnetite films are promising candidates for room temperature spintronic devices such as highly spin-polarized electrodes for magnetic tunneling junctions [7,8,9] or spin injectors [10]. Furthermore, multilayers of magnetite and platinum show huge thermoelectric effects [11] based on the recently observed spin Seebeck effect in magnetite [12] pushing the development of more efficient thermoelectric nanodevices [13].…”

Section: Introductionmentioning

confidence: 99%

Impact of Strain and Morphology on Magnetic Properties of Fe3O4/NiO Bilayers Grown on Nb:SrTiO3(001) and MgO(001)

et al. 2018

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We present a comparative study of the morphology and structural as well as magnetic properties of crystalline Fe3O4/NiO bilayers grown on both MgO(001) and SrTiO3(001) substrates by reactive molecular beam epitaxy. These structures were investigated by means of X-ray photoelectron spectroscopy, low-energy electron diffraction, X-ray reflectivity and diffraction, as well as vibrating sample magnetometry. While the lattice mismatch of NiO grown on MgO(001) was only 0.8%, it was exposed to a lateral lattice mismatch of −6.9% if grown on SrTiO3. In the case of Fe3O4, the misfit strain on MgO(001) and SrTiO3(001) amounted to 0.3% and −7.5%, respectively. To clarify the relaxation process of the bilayer system, the film thicknesses of the magnetite and nickel oxide films were varied between 5 and 20 nm. While NiO films were well ordered on both substrates, Fe3O4 films grown on NiO/SrTiO3 exhibited a higher surface roughness as well as lower structural ordering compared to films grown on NiO/MgO. Further, NiO films grew pseudomorphic in the investigated thickness range on MgO substrates without any indication of relaxation, whereas on SrTiO3 the NiO films showed strong strain relaxation. Fe3O4 films also exhibited strong relaxation, even for films of 5 nm thickness on both NiO/MgO and NiO/SrTiO3. The magnetite layers on both substrates showed a fourfold magnetic in-plane anisotropy with magnetic easy axes pointing in 100 directions. The coercive field was strongly enhanced for magnetite grown on NiO/SrTiO3 due to the higher density of structural defects, compared to magnetite grown on NiO/MgO.

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Section: Introductionmentioning

confidence: 99%

Impact of Strain and Morphology on Magnetic Properties of Fe3O4/NiO Bilayers Grown on Nb:SrTiO3(001) and MgO(001)

et al. 2018

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“…Thus, the underlying electronic and magnetic structure determining the properties of the magnetite thin film in question or the tunnel magneto resistance in magnetic tunnel junctions with magnetite electrodes. 15,16,17,18 Potential approach to minimize or suppress Mg segregation, besides rather low substrate temperatures during magnetite growth, is an additional buffer layer, e.g. metallic iron 19 or NiO 20 between the Fe 3 O 4 and the substrate.…”

Section: Introductionmentioning

confidence: 99%

FromFe3O4/NiO bilayers toNiFe2O4-like thin films through Ni interdiffus

et al. 2016

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Ferrites with (inverse) spinel structure display a large variety of electronic and magnetic properties making some of them interesting for potential applications in spintronics. We investigate the thermally induced interdiffusion of Ni 2+ ions out of NiO into Fe3O4 ultrathin films resulting in off-stoichiometric nickelferrite-like thin layers. We synthesized epitaxial Fe3O4/NiO bilayers on Nb-doped SrTiO3(001) substrates by means of reactive molecular beam epitaxy. Subsequently, we performed an annealing cycle comprising three steps at temperatures of 400• C, 600• C, and 800• C under an oxygen background atmosphere. We studied the changes of the chemical and electronic properties as result of each annealing step with help of hard x-ray photoelectron spectroscopy and found a rather homogenous distribution of Ni and Fe cations throughout the entire film after the overall annealing cycle. For one sample we observed a cationic distribution close to that of the spinel ferrite NiFe2O4. Further evidence comes from low energy electron diffraction patterns indicating a spinel type structure at the surface after annealing. Site and element specific hysteresis loops performed by x-ray magnetic circular dichroism uncovered the antiferrimagnetic alignment between the octahedral coordinated Ni 2+ and Fe 3+ ions and the Fe 3+ in tetrahedral coordination. We find a quite low coercive field of 0.02 T, indicating a rather low defect concentration within the thin ferrite films.

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“…In case of MgO tunnel barriers adjacent to magnetite electrodes, the interdiffusion of the magnesium ions during annealing affects the magnitude and the sign of the TMR. 24 The magnesium interdiffusion can be reduced, and higher annealing temperatures for magnetite are possible if iron buffer layers are deposited on the MgO substrate prior to the deposition of the magnetite films. 25 Here, a 10 nm iron film functions as a sacrificing layer that is completely oxidized after the annealing process at higher temperatures, while the surface near region of the 10 nm overlaying magnetite film remains unaffected by the Mg interdiffusion.…”

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Modifying magnetic properties of ultra-thin magnetite films by growth on Fe pre-covered MgO(001)

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Krampf

Bertram³

et al. 2015

Journal of Applied Physics

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Iron oxide films were reactively grown on iron buffer films, which were deposited before on MgO(001) substrates to analyze the influence of the initial iron buffer layers on the magnetic properties of the magnetite films. X-ray photoelectron spectroscopy and low energy electron diffraction showed that magnetite films of high crystalline quality in the surface near region were formed by this two-step deposition procedure. The underlying iron film, however, was completely oxidized as proved by x-ray reflectometry and diffraction. The structural bulk quality of the iron oxide film is poor compared to magnetite films directly grown on MgO(001). Although the iron film was completely oxidized, we found drastically modified magnetic properties for these films using the magnetooptic Kerr effect. The magnetite films had strongly increased coercive fields, and their magnetic in-plane anisotropy is in-plane rotated by 458 compared to magnetite films formed directly by one step reactive growth on MgO(001). V C 2015 AIP Publishing LLC.

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Sign change in the tunnel magnetoresistance of Fe3O4/MgO/Co-Fe-B magnetic tunnel junctions depending on the annealing temperature and the interface treatment

Cited by 22 publications

References 42 publications

Impact of Strain and Morphology on Magnetic Properties of Fe3O4/NiO Bilayers Grown on Nb:SrTiO3(001) and MgO(001)

Impact of Strain and Morphology on Magnetic Properties of Fe3O4/NiO Bilayers Grown on Nb:SrTiO3(001) and MgO(001)

FromFe3O4/NiO bilayers toNiFe2O4-like thin films through Ni interdiffus

Modifying magnetic properties of ultra-thin magnetite films by growth on Fe pre-covered MgO(001)

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